linux-kernel - Re: [PATCH] x86/mce: timer must be setup unconditionally

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Message-ID: <4B1629A0.60403@jp.fujitsu.com>
Date:	Wed, 02 Dec 2009 17:47:28 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Jan Beulich <JBeulich@...ell.com>
CC:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	stable@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mce: timer must be setup unconditionally

Jan Beulich wrote:
> mce_timer must be passed to setup_timer() in all cases, no matter
> whether it is going to be actually used. Otherwise, when the CPU gets
> brought down, its call to del_timer_sync() will never return, as the
> timer won't have a base associated, and hence lock_timer_base() will
> loop infinitely.

No, what we need to fix is hotplug callbacks.
So correct fix should be like "del/add timer conditionally when hotplug."

Thanks,
H.Seto

> (Patch applying to -tip is attached.)
> 
> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
> Cc: <stable@...nel.org>
> 
> ---
>  arch/x86/kernel/cpu/mcheck/mce.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> --- linux-2.6.32-rc8/arch/x86/kernel/cpu/mcheck/mce.c
> +++ 2.6.32-rc8-x86-mce-setup-timer-always/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -1374,13 +1374,14 @@ static void mce_init_timer(void)
>  	struct timer_list *t = &__get_cpu_var(mce_timer);
>  	int *n = &__get_cpu_var(mce_next_interval);
>  
> +	setup_timer(t, mcheck_timer, smp_processor_id());
> +
>  	if (mce_ignore_ce)
>  		return;
>  
>  	*n = check_interval * HZ;
>  	if (!*n)
>  		return;
> -	setup_timer(t, mcheck_timer, smp_processor_id());
>  	t->expires = round_jiffies(jiffies + *n);
>  	add_timer_on(t, smp_processor_id());
>  }

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